Tocopherols Protect Synechocystis sp. Strain PCC 6803 from Lipid Peroxidation

Tocopherols (vitamin E) are lipid-soluble antioxidants synthesized only by photosynthetic eukaryotes and some cyanobacteria, and have been assumed to play important roles in protecting photosynthetic membranes from oxidative stress. To test this hypothesis, tocopherol-deficient mutants of Synechocystis sp. strain PCC 6803 (slr1736 and slr1737 mutants) were challenged with a series of reactive oxygen species-generating and lipid peroxidation-inducing chemicals in combination with high-light (HL) intensity stress. The tocopherol-deficient mutants and wild type were indistinguishable in their growth responses to HL in the presence and absence of superoxide and singlet oxygen-generating chemicals. However, the mutants showed enhanced sensitivity to linoleic or linolenic acid treatments in combination with HL, consistent with tocopherols playing a crucial role in protecting Synechocystis sp. strain PCC 6803 cells from lipid peroxidation. The tocopherol-deficient mutants were also more susceptible to HL treatment in the presence of sublethal levels of norflurazon, an inhibitor of carotenoid synthesis, suggesting carotenoids and tocopherols functionally interact or have complementary or overlapping roles in protecting Synechocystis sp. strain PCC 6803 from lipid peroxidation and HL stress.